Well actually… 🤓

According to this Stackexhange answer to a similar question there’s a sort of semi-official Starfleed Academy Training Manual that had “extensive involvement” from the production staff but is ultimately fan-made, and it has this to say about facial hair:

Starfleet uniform regulations require that men keep faces shaven, except that a short, neat moustache/beard is permitted. No unusual beards or moustaches are permitted. Men must keep their hair neatly and closely trimmed, length not to exceed seven centimetres. Women must keep their hair neatly arranged, with back hair touching but not falling below the collar. Side hair must be trimmed to show a close contour.

And I mean, considering that Starfleet is essentially a military organization (or paramilitary at best), I’d be really surprised if they didn’t have grooming standards.